plug compatible

Before the rise of the PCM peripheral industry, computing systems were either configured with peripherals designed and built by the CPU vendor,{{cite book|author=Herbert Hovenkamp|url=https://books.google.com/books?isbn=1640200827|title=Principles of Antitrust|date=2017|isbn=978-1640200821}} or designed to use vendor-selected rebadged devices.

The first example of plug-compatible IBM subsystems were tape drives and controls offered by Telex beginning 1965.{{cite book |author=Pugh |title=IBM's 360 and Early 370 Systems |url=https://archive.org/details/ibms360early370s0000pugh |url-access=registration |page=[https://archive.org/details/ibms360early370s0000pugh/page/233 233] |date=1991 |publisher=MIT Press |isbn=9780262161237 |display-authors=etal}} Memorex in 1968 was first to enter the IBM plug-compatible disk followed shortly thereafter by a number of suppliers such as CDC,"Expected to produce $1 billion in revenues during fiscal 1980, CDC's peripherals business, advancing at 33% annually, is the fastest growing revenue producer within the company's diverse product line."{{cite news |newspaper=Computerworld |date=August 18, 1980 |page=7 |url=https://books.google.com/books?id=vpGNJfMmFswC |title=CDC PCM Peripherals - $1 Billion market}} Itel, and Storage Technology Corporation. This was boosted by the world's largest user of computing equipment"GSA has initiated a Government-wide program.to replace existing leased peripheral devices with lower cost plug-to-plug compatible equipment offered by independent suppliers. This program was aimed at permitting competitive offers of peripherals by independent suppliers."{{cite book |title=The Creative Partnership: Government and the Professional Services |url=https://books.google.com/books?id=tO9pQR81nooC |date=1973}} in both directions."... to allow the use of IBM plug-compatible peripherals on the CDC 6400, 6600 and 7600 systems installed at the LBL Computer Center. This has given the ability to replace unreliable CDC tape drives and controllers and overpriced CDC disk drives and controllers with their IBM plug-compatible counterparts."{{cite web |title=For Reference |url=https://pubarchive.lbl.gov/islandora/object/ir%253A104692/datastream/PDF/download/citation.pdf}}

Ultimately plug-compatible products were offered for most peripherals and system main memory.{{cite web|url=http://www.bitsavers.org/pdf/charlesRiverAssoc/US_vs_IBM_Exhibit_14971_part_2_Jul80.pdf|title=Historical Narrative Statement of Richard B. Mancke, Franklin M. Fisher and James W. McKie, Exhibit 14971, US vs. IBM, Part 2|pages=750–796|date=July 1980}}

A plug-compatible machine is one that has been designed to be backward compatible with a prior machine. In particular, a new computer system that is plug-compatible has not only the same connectors and protocol interfaces to peripherals, but also binary-code compatibility—it runs the same software as the old system. A plug compatible manufacturer or PCM is a company that makes such products.

One recurring theme in plug-compatible systems is the ability to be bug compatible{{cite web |title=bug-for-bug compatible |url=http://www.catb.org/jargon/html/B/bug-for-bug-compatible.html|quote = Same as bug-compatible, with the additional implication that much tedious effort went into ensuring that each (known) bug was replicated.|website = The Jargon File|publisher= Eric S. Raymond}} as well. That is, if the forerunner system had software or interface problems, then the successor must have (or simulate) the same problems. Otherwise, the new system may generate unpredictable results, defeating the full compatibility objective. Thus, it is important for customers to understand the difference between a "bug" and a "feature", where the latter is defined as an intentional modification to the previous system (e.g. higher speed, lighter weight, smaller package, better operator controls, etc.).

The original example of PCM mainframes was the Amdahl 470 mainframe computer which was plug-compatible with the IBM System 360 and 370, costing millions of dollars to develop. Similar systems were available from Comparex, Fujitsu,"LEAD: Beating I.B.M. to the punch by one day, Fujitsu Ltd. announced a series of computers today that ..."{{cite web |website=The New York Times |title=Fujitsu Announces Mainframe |url=https://www.nytimes.com/1990/09/05/business/fujitsu-announces-mainframe.html |date=September 5, 1990}} and Hitachi. Not all were large systems."A 3200 system can include up to 16M bytes, with virtual memory freeing programmers from artificial memory constraints. It can handle all major programming languages, such as Cobol, Fortran, PL/I, APL, Basic, and Assembler. The NCSS 3200 series will range in price from $200,00 to $600,000."{{cite journal |title=NCSS 3200|doi=10.1109/C-M.1978.217954}}Trilogy Systems Corporation was started by Gene Amdahl together with his son Carl Amdahl and Clifford Madden.{{cite news |newspaper=Computerworld |date=June 15, 1981 |url=https://books.google.com/books?id=dPLZ7QidjbEC |page=11 |title=ACSYS - new Amdahl startup}} Most of these system vendors eventually left the PCM market.{{Cite magazine |last=Greenwald |first=John |date=1983-07-11 |title=The Colossus That Works |url=http://content.time.com/time/magazine/article/0,9171,949693-2,00.html |url-status=live |url-access=subscription | magazine=TIME |archive-url=https://web.archive.org/web/20080514004334/http://www.time.com/time/magazine/article/0,9171,949693-2,00.html |archive-date=2008-05-14 |access-date=2019-05-18}}"Hitachi has been in the mainframe business for 50 years and currently its AP series of systems are sold to major organisations across Japan. Hitachi Data Systems used to sell Hitachi-made IBM plug-compatible mainframes outside Japan but stopped doing so in 2000."{{cite news |newspaper=The Register |date=May 24, 2017 |title=Hitachi exits mainframe hardware business |url=https://www.theregister.co.uk/2017/05/24/hitachi_exits_mainframe_hardware}}"A notable PCM failure was Storage Technology (StorageTek), which was for many years one of the more successful of the plug-compatible peripheral suppliers. StorageTek's attempt to make its own processor and become another Amdahl or HDS almost drove it out of business. It took years to recover ..."{{cite web |title=ACS Heritage Project: Chapter 30 |url=https://ia.acs.org.au/article/2017/ACS-Heritage-Project--Chapter-30.html}}"Amdahl ...pulling out of the plug-compatible market in 2000 following IBM's launch of 64-bit systems."{{cite news |newspaper=Computerworld |title=Amdahl pulling out of the plug-compatible market in 2000 |url=https://www.computerworld.com/article/2589047/vertical-it/amdahl-planning-to-exit-mainframe-business.html}} In late 1981, there were eight PCM companies, and collectively they had 36 IBM-compatible models.{{cite magazine |magazine=Computer Decisions

|title=Plug Compatible Manufacturers: Splitting the Pie

|author=Elinor Gebremedhin |date=November 1981 |pages=119-124, 202-207}}

The term may also be used to define replacement criteria for other components"A universal four-contact plug and jack assembly ..."{{cite web |title=Patent US20040175993 - Universal audio jack and plug |url=https://patents.google.com/patent/US20040175993 |date=September 9, 2004}} available from multiple sources. For example, a plug-compatible cooling fan may need to have not only the same physical size and shape, but also similar capability, run from the same voltage, use similar power, attach with a standard electrical connector, and have similar mounting arrangements. Some non-conforming units may be re-packaged or modified to meet plug-compatible requirements, as where an adapter plate is provided for mounting, or a different tool and instructions are supplied for installation, and these modifications would be reflected in the bill of materials for such components. Similar issues arise for computer system interfaces when competitors wish to offer an easy upgrade path.

In general, plug-compatible systems are designed where industry or de facto standards have rigorously defined the environment, and there is a large installed population of machines that can benefit from third-party enhancements. Plug compatible does not mean identical replacement. However, nothing prevents a company from developing follow-on products that are backward-compatible with its own early products.

• Bug compatibility
• Clone (computing)
• Computer compatibility
• Drop-in replacement
• Hercules (emulator)
• Pin compatibility
• Proprietary hardware
• Vendor lock-in
• Honeywell 200, chasing the IBM 1401 market
• Xerox 530, chasing the IBM 1130 market

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Category:Classes of computers

Category:Computer hardware

Category:Interoperability